Devereux was the product of an illicit union between the 2nd earl of Essex and one of the queen’s maids, Elizabeth Southwell, the daughter of a Norfolk squire. Southwell’s pregnancy - coyly referred to as a ‘lameness in her leg’ by one observer - aroused the queen’s anger, whereupon responsibility was pinned on a minor courtier named Thomas Vavasour (probably the gentleman pensioner of that name who had served with Essex in the Netherlands), who was briefly imprisoned.
Following Essex’s execution, and perhaps even beforehand, Devereux was entrusted to his paternal grandmother, Lettice, countess of Leicester, at her Staffordshire seat of Drayton Bassett. In November 1604, aged about 13, he was sent to Oxford, where he contributed to a collection of Latin verses composed to commemorate the visit to the university in 1606 of Christian IV of Denmark.
In September 1613 Devereux journeyed to the Netherlands in company with Essex after the earl challenged Henry Howard*, a younger son of the 1st earl of Suffolk, to a duel for disparaging Essex’s estranged wife. Devereux was appointed one of Essex’s seconds, but before the duel could be fought the protagonists were ordered to return to England by the king. When the Privy Council attempted to establish the facts of the case Devereux initially proved obstructive by failing to pass on as promised a message to his fellow second, Richard Ouseley.
Devereux was returned to Parliament in March 1614 for Pembroke Boroughs, but left no mark on its records. He perhaps owed his seat to Essex, although Lamphey manor lay only a few miles from Pembroke. In September 1617 he was knighted at Ashby-de-la-Zouch, home of the Hastings family. He sold Lamphey manor to Richard Cuny* in November 1618, whereupon Essex bestowed upon him the lease of Lamphey rectory.
Shortly after the 1624 Parliament was prorogued, Essex and Devereux travelled to the Netherlands, where the earl took up the colonelcy of an infantry regiment and bestowed a captaincy on Devereux. In July 1625 the two brothers returned to England, where Essex was given command of a squadron of ships which were preparing to sail as part of an expeditionary force to Spain. However, no place was found for Devereux in the list of infantry captains,
Devereux accompanied Essex to Ireland in 1633.
Devereux was elected to both the Short and the Long Parliaments as the senior burgess for Lichfield, presumably on his brother’s interest. He died intestate in July 1641 at Essex House, in the Strand, and was buried nearby in the church of St. Clement Danes.
